How to install helicoil inserts

Updated July 20, 2017

Stripping out the threads in a bolt hole can be extremely frustrating. In some cases you could drill out the hole and tap it to the next size up, but due to space restrictions or other factors, this is not always feasible. When you can't go to the next size hole, your only option is to repair the threads. Thanks to the HeliCoil thread insert kit, you can repair the hole with little fuss.

Drill out the hole with an electric drill and drill bit of the size specified by the HeliCoil kit. You will need to know the size and thread pitch of the hole you are repairing, for instance, a 3/8-inch diameter bolt with 16 threads per inch, or a 10mm diameter bolt with a 1.25 thread pitch. Drill slightly deeper than the length of the bolt that goes in the hole.

Insert the tap tool from the HeliCoil kit into the drilled hole and begin turning the tap. Keep the tap centred in the hole. Tap out the hole to the depth you drilled. The tap will cut new threads in the hole.

Spray the hole with carburettor cleaner to clear out any metal shavings.

Screw your HeliCoil insert, which is called a mandrel, onto the installing tool. The insert has a tang at the end. It looks like the end of the insert is bent so it blocks the centre of the insert. When you screw the insert onto the mandrel, the tang will catch in the notch in the end of the mandrel. This allows you to screw the insert into the new hole.

Use the mandrel to screw the insert into the new hole until the insert is one to one and one-half threads below the surface. The threads on the outside of the insert match the new threads in the hole; the threads on the inside of the insert match the old threads.

Remove the mandrel by unscrewing it. Insert the tang-removal tool, which looks like a metal rod, into the hole and strike the tool with a hammer to break off the tang.

Things You'll Need

  • Electric Drill
  • Drill bit (size specified by HeliCoil kit)
  • HeliCoil kit
  • Carburettor cleaner
  • Hammer
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About the Author

Robert Bayly, based in Apple Valley, California, began writing in 2010, his "how to" articles can be found on eHow. With more than 15 years in the auto industry, Bayly has been an auto and diesel mechanic, service writer and parts manager. He received certificates from Pontiac (parts system), Cat Diesel (engine service), Saab and Fiat (parts- warranty system).